Polyallyl ethers derived from polyols and carbohydrates, particularly allylated pentaerythritol, trimethylpropane, and starches and sugars have been widely investigated as monomers suitable for protective coatings. These materials are attractive since they undergo autoxidative polymerization in contact with air. However, because of slow curing rates, color formation and relatively poor substrate bonding strength, films of these allyl ethers have limited commercial use (see ALLYL COMPOUNDS AND THEIR POLYMERS by C. E. Schildknecht, Wiley Interscience, 1973). Additionally many of these monomers and oligomers are thermally unstable and decompose to give off an objectionable odor characteristic of acrolein.
Attempts to prepare high molecular weight monoallyl ethers by free radical or ionic polymerizations have not been successful and result in low molecular weight product in admixture with substantial quantities of unreacted material which is difficult to separate. According t to British Patent 730,670, the polymerization of a allyl glycidyl ether benzene solution in the presence of 3% ditertiary butyl peroxide at 155.degree. C. resulted in a product having a molecular weight of only 500 which was contaminated with a significant quantity of unconverted allyl glycidyl ether. Obviously such materials are unsuitable as protective coatings.
Although esters, which are electron accepting and require free radical initiation for UV curing, are not comparable to electron donating ethers which are highly reactive in cationically induced reactions, it is noted for the sake of full disclosure that certain ester blends of acrylated bisphenol A epoxy resins and ester blends of acrylated aromatic urethanes have been cured by UV exposure to provide rigid coatings. This work is reported by Byron K. Christmas et al. in 1988 (Specialty Chemicals 8(1) 24-6). However, these ester blends are not UV curable by cationically induced systems. Thus, as to be expected, their curing rates are comparatively slow, i.e. 7.5-100 ft/min with few exceptions up to 150 ft/min as compared to 300-500 ft/min achieved with cationically initiated UV radiation. Also, the coating properties of these blends display highly unpredictable results ranging from 0%-100% adhesion and MEK resistance from 1 to about 50 in most cases.
Accordingly, it is an object of the present invention to avoid the use of esters and to overcome the above deficiencies by the use of certain alkenyl derived ethers which are readily polymerizable in cationically initiated systems to provide thermally stable compounds having superior coating properties.
Another object is to provide films which consistently show good adhesion and high resistance to chemical attack.
Another object of this invention is to provide an economical and commercially feasible process for rapid curing of coated materials.
Still another object is to provide metal and glass coatings and finishes which are not subject to coloration over extended periods of use.
These and many other objects of the invention will become apparent from the following description and disclosure.